In a typical cellular radio system, also referred to as a wireless communication system, user equipments, also known as mobile terminals and/or wireless terminals communicate via a Radio Access Network (RAN) to one or more core networks. The user equipments can be mobile stations or user equipment units such as mobile telephones also known as “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called “eNB”, “NodeB” or “B node” and which in this document also is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. The base stations communicate over the air interface operating on radio frequencies with the user equipment units within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a Radio Network Controller (RNC). The radio network controller, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies such as High Speed Packet Access (HSPA). In the end of 2008 the first release, Release 8, of the 3GPP Long Term Evolution (LTE) standard was finalized and the release 9 is currently going on.
Orthogonal Frequency-Division Multiple Access (OFDMA) is a common downlink multi-access method in many wireless broadband systems contemplated for the future, such as 3GPP-Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX). One of the main advantages of OFDMA is that user equipments can be scheduled for transmission and reception precisely in the specific time and frequency slots where they have good channel gains.
One basic feature of OFDMA is that all user equipments have to be informed which sub-carriers that they have been assigned for communicating with a base station over the air interface, and possibly what OFDM symbols in time, if the system uses time scheduling. This requires signalling of control information comprising of scheduling maps, so that the user equipments know which resource blocks in the time and frequency space to receive. Furthermore, the RBS typically informs the user equipments which transport formats such as e.g. coding and modulation, the downlink data is conveyed with. In this document, the scheduling maps and transport formats are denoted to be the so called scheduling information, which the RBS signals to the user equipments.
In LTE, the scheduling information is signalled dedicated to each user equipment on the Physical Downlink Control Channel (PDCCH), which PDCCH share the same downlink time, frequency and transmission power resources as the shared channel carrying the user data (PDSCH).
Wideband Code Division Multiple Access (WCDMA) is another multi-access method, where users receive their data on different downlink channelization codes. In High-Speed Downlink Packet Access (HSDPA), where all users share the same High-Speed Downlink Shared Channel (HS-DSCH) for data, they also need to be informed about the scheduling information, i.e. the downlink channelization codes and the transport format of the transmission. So here, the scheduling information comprises HS-DSCH channelization code and transport format, which is signalled on the High Speed Shared Control Channel (HS-SCCH). This signalling share the same downlink channelization code and base station power resources as the data on HS-DSCH.
In both LTE and WCDMA, it is the task of a downlink scheduler in a base station to divide the total power, time and frequency, or channelization code resources between user equipments need, i.e. to schedule the data and signalling to each user onto the sub-carriers for each time slot. This is typically done based on scheduling priority composed of several factors, such e.g.:                User equipment channel quality. User equipments with better relative channel quality are prioritized. A user equipment reported channel quality may be seen as an estimate of the user equipment's data throughput on the corresponding radio resource, if scheduled.        Radio access bearer priority. Bearers carrying signalling, emergency calls, etc. are prioritized.        Service requirements, through the Quality of service Class Indicator (QCI)        User priority. “Gold subscriptions” are prioritized.        Delay. Data packets from delay-sensitive services are prioritized when the packets are close to reach their critical delay limit.        Interference coordination        
Etc.
Experience from LTE simulations has shown that the overhead associated with the signalling of scheduling information to all user equipments can be substantial. In particular if many user equipments are scheduled in the same time slot. This means that transmission of such scheduling information consumes resources that could otherwise have been used for payload data.
In WCDMA, the scheduling information is signaled on the HS-SCCH, which has the capability to signal scheduling information to at the most four user equipments per time slot. So signalling scheduling information consumes base station transmission power for each user equipment, but also an additional channelization code with spreading factor 128 for each 4th additional user equipment to be scheduled.
In state of the art schedulers, this consummation of signalling power is not considered when choosing which user equipments to schedule on each sub-carrier i.e.
channelization code in HSDPA, for each slot. As described above, the estimated user throughput is instead typically based solely on the user equipment measured and reported channel quality for the various sub-carriers in LTE, i.e. for the whole bandwidth in WCDMA. This makes the scheduling decisions, also with respect to physical layer throughput, while different scheduling information require different amount of signalling radio resources, leaving different amount of available radio resources for the actual payload data to be conveyed.
For example, the well-known max-SIR scheduler, where the user with the best estimated Signal-to-Noise and Interference Ratio (SIR) is scheduled, which for every sub-carrier and time slot in LTE, schedules the user equipment having the largest signal-to-interference ratio, is generally known for maximizing the system's physical layer throughput. However, that is not generally true since max-SIR scheduling often yields a fragmented scheduling map with many user equipments scheduled each time slot, which consumes a lot of power to signal to the user equipments.